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HP-28S battery door
09-04-2018, 07:30 PM
Post: #1
HP-28S battery door
I've acquired a HP-28S in pretty much mint condition (datecode 2948), it really is unbelievable. Must not have been used.

Anyway, the battery door and body plastic around the opening do not appear to show any signs of stress or cracks whatsoever.

Ideas on how do I can avoid the battery door issue? I know I could just not use the calculator and sure enough it won't be my daily-driver anyway. But, I'd rather not just park the thing in a plastic bag and not be used, even lightly.
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09-04-2018, 08:05 PM (This post was last modified: 09-04-2018 08:06 PM by Zaphod.)
Post: #2
RE: HP-28S battery door
(09-04-2018 07:30 PM)jonese Wrote:  I've acquired a HP-28S in pretty much mint condition (datecode 2948), it really is unbelievable. Must not have been used.

Anyway, the battery door and body plastic around the opening do not appear to show problems But, I'd rather not just park the thing in a plastic bag and not be used, even lightly.

Nothing HP28 specific from me, Just general fragile and ageing plastic advice:

Keep it away from sunlight , and don’t open it unless you’re in warm surroundings.... and be gentle with it when opening the battery door.
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09-04-2018, 08:31 PM
Post: #3
RE: HP-28S battery door
Hello!

(09-04-2018 07:30 PM)jonese Wrote:  Ideas on how do I can avoid the battery door issue? .

There is really only one thing you can do: Don't put batteries inside. I recently got another HP-19BII which looked as unused as yours. I wanted to put batteries inside to see if it works. As soon as I was about to close the battery door, the brown plastic started to turn white from the strain. One little more push and it would have cracked.

On this forum there are some tips about how to reduce the strain on the battery door. Among them:
. Look for the smallest possible N-cells. Not easy as one can be lucky to find these batteries at all.
. Put some tape around the cells to increase the friction inside the calculator housing thereby reducing the pressure on the battery door. Might actually work, however the correct amount of tape will be difficult to find out. Not enough and one achieves nothing, too much and the cells won't make contact. And in the worst case they may split the calculator housing, In any case they will be very difficult to remove.
. Replace the springs with weaker ones or cut off a couple of windings from the springs installed. Might work, but one has to take the calculator apart for that after which it will never be as before again.
- Power it from an external source through some self made battery replacements. This requires some DIY skills and will turn the machine from pocket to desktop calculator.

Maybe I missed some other options?

Regards
Max
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09-04-2018, 09:17 PM (This post was last modified: 09-04-2018 09:19 PM by burkhard.)
Post: #4
RE: HP-28S battery door
(09-04-2018 07:30 PM)jonese Wrote:  Ideas on how do I can avoid the battery door issue?

I understand what Maximilian is saying with respect to tape and the batteries, but in order for that to work, they are going to be really hard to take out as well. It seems tough to achieve the "sweet spot" and difficult to extract the batteries when they need extracting.

I had considered (but haven't tried it yet) trying either a flat top N or possibly even a flat top 2/3 AAA instead of the normal N. The normal "N" battery should be slightly shorter (better) than a normal "2/3 AAA", but a flatop "2/3 AAA" might be slightly shorter (better) than the normal "N", helping to reduce the static loading of the door:body interface. I haven't confirmed the measurements yet, though.

In the interim, any time I need to open to battery compartment, I actually press the door in a little while I'm sliding it. This is a bit counter intuitive, but allow me to explain. While this compresses the springs a bit more, it stops the door from sliding against the case. That door:case sliding under pressure is bad news; it acts on the stress risers designed into the interface and allows cracks to start and propagate readily. Avoid the stress at the interface and things are a lot safer, IMO.

It sounds obvious, but DON'T drop it on the floor. One good hit there while the battery springs are pressing on everything and it's "Goodnight, Irene" as my uncle used to say. They can't handle the shock on top of the normal battery load.

It seems most HP calculator models have at least one crappy design aspect. This is it for the clamshells.

Good luck!
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09-04-2018, 09:20 PM
Post: #5
RE: HP-28S battery door
Purchase a door in the back model for the HP-19BII (sorry 18c, 28C & 28S owners). I have primaries and spares for the entire clamshell range, including extra d-i-t-b 19BII.

Maybe someone will create a replacement shell with a door in the back with srew mount face-plate connectors? till then …

BEST!
SlideRule
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09-05-2018, 01:53 AM (This post was last modified: 09-05-2018 01:57 AM by Jlouis.)
Post: #6
RE: HP-28S battery door
(09-04-2018 09:20 PM)SlideRule Wrote:  Purchase a door in the back model for the HP-19BII (sorry 18c, 28C & 28S owners). I have primaries and spares for the entire clamshell range, including extra d-i-t-b 19BII.

Maybe someone will create a replacement shell with a door in the back with srew mount face-plate connectors? till then …

BEST!
SlideRule

There's a guy in Curitiba, Brazil, that modifies the clamshell calculator, putting the batteries on the back. I just saw photos, but looks like it was made by HP. I 've bought calculators from him, but never bought one modified. He sold recently one 19bII with the modified back door for the equivalent of 100 us dollars.

I have no affiliation with him in whatever way.

Here is a link for an advertisement.

Ask him for some photos, you will be amazed.

If you need some help with Portuguese, just let me know.

Edit: the last photo in the ad is a modified 19bII

Cheers

JL
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09-05-2018, 01:07 PM
Post: #7
RE: HP-28S battery door
(09-05-2018 01:53 AM)Jlouis Wrote:  There's a guy in Curitiba, Brazil, that modifies the clamshell calculator, putting the batteries on the back. I just saw photos, but looks like it was made by HP. I 've bought calculators from him, but never bought one modified. He sold recently one 19bII with the modified back door for the equivalent of 100 us dollars.

I have no affiliation with him in whatever way.

Here is a link for an advertisement.

Ask him for some photos, you will be amazed.

If you need some help with Portuguese, just let me know.

Edit: the last photo in the ad is a modified 19bII

Cheers

JL

That's pretty neat work. I don't think I'd do his mod to a perfect clamshell, but to save a broken one from the junk drawer, it's great! Does his new door system retain N batteries or somehow go to something else, as in the "from the factory" batteries-on-the-back 19BII?
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09-05-2018, 02:35 PM
Post: #8
RE: HP-28S battery door
(09-05-2018 01:53 AM)Jlouis Wrote:  There's a guy in Curitiba, Brazil, that modifies the clamshell calculator, putting the batteries on the back. I just saw photos, but looks like it was made by HP. I 've bought calculators from him, but never bought one modified. He sold recently one 19bII with the modified back door for the equivalent of 100 us dollars.

I have no affiliation with him in whatever way.

Here is a link for an advertisement.
Thanks for sharing this JL, however, when I follow this link, I don't see any clamshell machines at all; do I need to navigate somehow from that page, and if so, what do I click?

--Bob Prosperi
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09-05-2018, 03:11 PM (This post was last modified: 09-05-2018 03:19 PM by Gerson W. Barbosa.)
Post: #9
RE: HP-28S battery door
(09-05-2018 02:35 PM)rprosperi Wrote:  
(09-05-2018 01:53 AM)Jlouis Wrote:  There's a guy in Curitiba, Brazil, that modifies the clamshell calculator, putting the batteries on the back. I just saw photos, but looks like it was made by HP. I 've bought calculators from him, but never bought one modified. He sold recently one 19bII with the modified back door for the equivalent of 100 us dollars.

I have no affiliation with him in whatever way.

Here is a link for an advertisement.
Thanks for sharing this JL, however, when I follow this link, I don't see any clamshell machines at all; do I need to navigate somehow from that page, and if so, what do I click?

Just take a look at the last two pictures.
I know him, BTW. I might visit him one of these days as the battery door of 28S needs repair.

PS.: Just talked to him. Here is the link to his website:

http://hpcenter.com.br
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09-05-2018, 04:03 PM
Post: #10
RE: HP-28S battery door
(09-05-2018 03:11 PM)Gerson W. Barbosa Wrote:  
(09-05-2018 02:35 PM)rprosperi Wrote:  Thanks for sharing this JL, however, when I follow this link, I don't see any clamshell machines at all; do I need to navigate somehow from that page, and if so, what do I click?

Just take a look at the last two pictures.

Maybe the web page looks different from Brazil? I only see 12Cs and accessories for Voyager calculators on that page when viewed from Britain.

— Ian Abbott
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09-05-2018, 04:14 PM
Post: #11
RE: HP-28S battery door
(09-05-2018 04:03 PM)ijabbott Wrote:  
(09-05-2018 03:11 PM)Gerson W. Barbosa Wrote:  Just take a look at the last two pictures.

Maybe the web page looks different from Brazil? I only see 12Cs and accessories for Voyager calculators on that page when viewed from Britain.

Better than pictures, you can find two Youtube videos here (Scroll down until the bottom of the page)
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09-05-2018, 06:11 PM
Post: #12
RE: HP-28S battery door
(09-05-2018 04:03 PM)ijabbott Wrote:  
(09-05-2018 03:11 PM)Gerson W. Barbosa Wrote:  Just take a look at the last two pictures.

Maybe the web page looks different from Brazil? I only see 12Cs and accessories for Voyager calculators on that page when viewed from Britain.

(09-05-2018 04:14 PM)Gerson W. Barbosa Wrote:  
(09-05-2018 04:03 PM)ijabbott Wrote:  Maybe the web page looks different from Brazil? I only see 12Cs and accessories for Voyager calculators on that page when viewed from Britain.

Better than pictures, you can find two Youtube videos here (Scroll down until the bottom of the page)

I agree with ijabbott, we are definitely seeing different pages, I see the same as him.

But, the Youtube video works just fine, one can easily see his repair method and the nice work he does. Always good to see the work of a real craftsman.

Thanks JL and Gerson.

--Bob Prosperi
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09-05-2018, 10:01 PM
Post: #13
RE: HP-28S battery door
Wow,

So it looks like he cements the damaged door and body area, permanently sealing it. Then then cuts out the back area out, shrinks it slightly, puts in a plastic post that can hold a new screw to secure the back area in place.

Drastic, but effective!
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09-06-2018, 01:26 AM
Post: #14
RE: HP-28S battery door
(09-05-2018 04:03 PM)ijabbott Wrote:  
(09-05-2018 03:11 PM)Gerson W. Barbosa Wrote:  Just take a look at the last two pictures.

Maybe the web page looks different from Brazil? I only see 12Cs and accessories for Voyager calculators on that page when viewed from Britain.

Well, his AD from the link I post is gone, this is not a geo issue.

Don't know why he removed his AD.

But Gerson link from his site and the youtube videos did the trick, this is what matters.

As a said, i bought some calculators from him and everything was ok.

I have many clanshells but all with a nice battery door, so I think I will skip this for a
while

Cheers
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09-06-2018, 03:02 AM (This post was last modified: 09-06-2018 03:06 PM by burkhard.)
Post: #15
RE: HP-28S battery door
(09-04-2018 09:17 PM)burkhard Wrote:  
(09-04-2018 07:30 PM)jonese Wrote:  Ideas on how do I can avoid the battery door issue?

I had considered (but haven't tried it yet) trying either a flat top N or possibly even a flat top 2/3 AAA instead of the normal N. The normal "N" battery should be slightly shorter (better) than a normal "2/3 AAA", but a flatop "2/3 AAA" might be slightly shorter (better) than the normal "N", helping to reduce the static loading of the door:body interface. I haven't confirmed the measurements yet, though.

OK, I just did confirm it. The "regular" alkaline Energizer N batteries HP expected you to use in the calculator I have measure 29.45 mm long. The "flat top" Chinese generic 2/3 AAA batteries I have measure 28.35 mm. So, each of the "flat top" 2/3 AAA is more than a millimeter shorter than the specified N batteries.

I tried out some of these "flat top" 2/3 AAA in a 28C just now and indeed there is noticably less pressure on the battery springs. Remember, the clamshells use 3 batteries, a stack of two and a single in parallel. So the stack of two side is ≈ 2.2mm shorter than a stack of two regular N batteries. That's noticeably less preload on the spring. I'm not sure if that substantially reduces the risk of side door area breakage, but it couldn't hurt.

They are a little smaller in diameter than N batteries as well, so no risk of getting stuck.

Oh yeah... as a bonus they seem to work OK as well. Everything seems to make contact... the calculator turns on and looks like it operates properly.

These are the exact batteries I have, purchased off eBay from a Canadian battery seller. They are *cheap*, only about $1US each *including* Canada → US shipping. They are NiMH as well, so rechargeable with the right adapters rigged up to get them to AAA length and preferably the charging current reduced somewhat.

"Flat Top" 2/3 AAA batteries as replacement for type N.
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